The present invention relates generally to tilt control mechanisms for chairs, and in particular, to synchrotilt control mechanisms.
In general, tilt control mechanisms are mechanical devices that control the tilting of a chair when occupied by a user. To provide improved aesthetics, and to avoid interference with use of the chair, tilt control mechanisms are typically mounted underneath the chair. Tilt control mechanisms also typically employ a spring, or other energy storing device, to control the rate at which the chair tilts and to return the chair to an upright position when the user is not leaning back in it. Tilt control mechanisms generally include an adjustment device that permits the user to vary the upward force exerted by the spring, thereby allowing the chair to tilt downwardly and rearwardly more or less easily depending on the upward force exerted.
Tilt chairs come in a variety of forms, although most include a seat and a back. For example, some tilt chairs have a seat maintained in a fixed position, allowing only the back to tilt rearwardly and downwardly. In another form, tilt chairs have the seat and back rigidly connected whereby they tilt rearwardly and downwardly at the same rate. Both of these types of chairs have disadvantages. For example, a fixed seat and back arrangement does not allow the user""s body cavity to open up as the user tilts rearwardly. An open body cavity allows for better circulation and spinal curvature, thereby improving the user""s comfort and physical health. Moreover, many of the previous designs pivot about a point near the base or support of the chair where the user""s center of gravity is located. As a result, when the chair is tilted rearwardly, the user""s feet are lifted off of the floor by the front part of the seat, thereby generating pressure on the underside of the user""s thighs, making the user uncomfortable and inhibiting the user""s circulation. Synchrotilt control mechanisms were designed to overcome some of these problems.
With synchrotilt mechanisms, the back and seat tilt simultaneously, but at different rates. Generally, the back tilts at a faster rate than the seat so that the body cavity opens. An example of a prior synchronous tilt control mechanism may be found in U.S. Pat. No. 4,390,206, entitled Synchrotilt Chair Control and issued to Faiks, et. al.
Typically, synchrotilt chairs have the seat and back interconnected so as to actuate the synchronized tilting of the back with the seat. For example, the seat and back may be directly pivotally connected as set forth in the Faiks, et. al. Patent. Other synchrotilt control mechanisms employ linkage mechanisms to interconnect the seat and back and to actuate the synchronous tilting. In either type, the synchrotilt control mechanism comprises complex interconnecting moving parts. The majority of these prior art tilt control mechanisms permit only backward tilting of the chair, separately or together at differing rates. To counter that problem, U.S. Pat. No. 5,029,940, entitled Chair Tilt and Chair Height Control Apparatus and issued to Golynsky, discloses a tilt mechanism permitting both forward and backward tilting of the chair seat and back using the same mechanism. That mechanism uses a four-bar linkage mechanism, whereby the seat is interconnected with the back. When the seat is tilted upwardly, the back of the chair is also caused to be tilted upwardly. Accordingly, the back can protrude into the user""s back thus making use in the forward tilt position uncomfortable.
Briefly stated, the invention is directed to a chair adapted for synchronous tilting between an upright position and a reclined position. In one aspect, the chair has a base, a tilt control housing, a seat, a back, a torsion spring, a first slide member, a second slide member and a tilt limiter device. The tilt control housing is mounted to the base. The seat is pivotally attached to the tilt control housing about a first horizontal axis. The back is pivotally attached to the tilt control housing about a second horizontal axis positioned rearwardly of the first horizontal axis. The back includes a forwardly extending support member. The torsion spring has a forwardly extending leg mounted to the tilt control housing and a rearwardly extending leg. The first slide member is disposed on one of the seat and support member and slidably engages the other of the seat and support member. The second slide member is disposed on one of the support member and the rearwardly extending leg of the torsion spring and engages the other of the support member and rearwardly extending leg. The tilt limiter device is adapted to limit upward tilting of the back.
Another aspect of the invention is to provide a tilt lock device to releasably lock the chair in a plurality of positions, including an upright position and a reclined position. The tilt lock device includes a lock member, a guide member having a guide hole and a lock pin slidably received in the guide hole. The lock member has a plurality of openings adapted to receive the lock pin and extends downwardly from the back support member. The guide member is mounted to the tilt control housing. When the tilt lock device is activated, the lock pin selectively engages the lock member at one of the openings.
In another aspect of the invention, the chair is adapted to permit a forward tilting of the seat without a corresponding forward tilting of the back. In a preferred embodiment, the seat can be maintained in the forward position by securing the seat with a stop device. Because the seat is not linked to the back, but only slidably engages it by way of the first slide member, the forward tilting of the seat does not simultaneously cause a forward tilting of the back. The back, therefore, does not protrude into the user""s back or otherwise interfere with the space located above the forwardly tilted seat.
Another aspect is for the horizontal axis of the torsion spring to be spaced apart from the second horizontal axis of rotation. Preferably, the axis of the spring is positioned below the second axis of rotation of the back such that the torsion spring exerts an increasingly greater upward force to counter any shift in the center of gravity of the user as the chair tilts rearwardly.
Yet another aspect of the invention is a seat depth mechanism, which permits the user to adjust the forward and rearward position of the seat with respect to the back of the chair. The mechanism includes a shell slidably attached to a seat bracket, a lever, a spring and a fastener. The shell includes a housing. The seat bracket has an adjustment slot and a plurality of teeth. The lever is disposed in the housing and is adapted to operably engage the spring which is also disposed in the housing. The lever is also adapted to engage the teeth of the seat bracket. When the lever is disengaged from the teeth, the user can slide the shell forward and rearward on the seat bracket until a desired positioning of the shell is achieved. When the lever is released by the user, the spring biases the lever inwardly to engage the teeth of the seat bracket, thereby preventing the shell from sliding in the forward or rearward direction.
The present invention provides significant advantages over other synchronous tilt mechanisms in that the synchronous tilt mechanism is simplified by using two slide members without the need for a complicated linkage mechanism. Furthermore, the tilt mechanism provides a device for locking the back and seat in a variety of positions. Finally, the simplified slide mechanism permits the seat of the chair to tilt forwardly and upwardly without the corresponding forward tilt of the back.
The present invention, together with further objects and advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.